Differential protection for transformers (starting from approx. 1 MVA), combined with time overcurrent protection, can be investigated using measurement techniques in normal operation, fault occurrences in various winding circuit configurations (star, delta), in various vector groups and as a function of star-point treatment (floating, direct or earthed using earth coils). In the case of differential currents, the tripping criteria is determined based on characteristic sensitivity.

The time overcurrent protection supplements the safety protection measures contained in transformer differential protection. It protects the transformers against short circuits outside the protection range and against overloading.

ETP 1 Transformer differential protection

Training contents:

• Detection and disconnection of transformer for internal faults
• Detection of peak inrush currents (RUSH) without disconnection
• Faulty tripping due to incorrectly dimensioned transformers
• Selection of tripping characteristics with differential currents taken into account

ETP 2 Time over-current protection

Training contents:

• Setting the parameters of the time overcurrent relay while taking the current transformation into consideration
• Detection of operating values for symmetrical and asymmetrical faults
• False tripping of the protective device during transformer’s switch-on response
• Transformer switch-on response in terms of protection